1. Field of the Invention
The present invention relates to optical communication equipment and, more specifically but not exclusively, to equipment for establishing and operating multiple-input/multiple-output (MIMO) optical-transport channels over a multimode or multi-core fiber.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
MIMO methods are being actively developed to exploit the inherently high transmission capacity of multimode and multi-core optical fibers. At a transmitter of an optical MIMO system, a plurality of optical signals are independently modulated with data and coupled into a corresponding plurality of spatial modes of a multimode or multi-core fiber for transmission to a remote receiver. At the receiver, the received optical signals carried by the plurality of spatial modes are separated from one another and demodulated/decoded to recover the data encoded onto the original optical signals at the receiver.
A representative multimode or multi-core fiber used in an optical MIMO system may have a relatively large number of (e.g., >100) spatial modes. Due to certain hardware limitations, a conventional transmitter may not be able to individually address all of the spatial modes supported by a typical multimode or multi-core fiber. For similar hardware reasons, a conventional receiver also may not be able to individually address all of those supported spatial modes. As a result, such a transmitter may not be able to simultaneously couple corresponding modulated optical signals into all of the supported spatial modes, and such a receiver may not be able to simultaneously extract corresponding modulated optical signals from all of the supported spatial modes. In addition, the subset of spatial modes addressed at the transmitter may differ from the subset of spatial modes addressed at the receiver. Disadvantageously, the optical noise and mode-dependent loss imposed by the fiber-optic link may cause the outage probability in such an under-addressed optical MIMO system to be relatively high.